1. Field of the Invention
The present invention is generally related to deployable structural assemblies and, more particularly, to generally elongated, deployable structural assemblies having a high bending stiffness to weight ratio, that are highly compact for storage purposes, are efficiently deployed and retracted, and are suitable for numerous uses.
2. State of the Art
It is often desirable to utilize a deployable structural assembly in various circumstances and environments. For example, deployable structural assemblies, sometimes referred to as deployable booms, may be utilized in conjunction with satellites or other aerospace vehicles. In many instances, the rigors of launching a satellite or aerospace vehicle make it impractical to have a structural assembly in an already-deployed condition or as a permanent installation such that it is extending or protruding from the vehicle during launch. Thus, it is often desirable to delay the deployment of a structural assembly until the satellite or vehicle with which it is associated is in a stable flight pattern, or is in orbit, or until the structural assembly is needed for a specific purpose.
Even after an aerospace vehicle has been placed in a stable flight pattern or in orbit, it may not be desirable to continually maintain a structural assembly in a deployed state. Thus, it becomes desirable to utilize a structural assembly that is capable of being deployed and retracted, relative to the satellite or aerospace vehicle, when desired or on demand. Such a structural assembly may be utilized to deploy, for example, solar sails or solar shields in association with a satellite after the satellite is placed in orbit. Deployable structural assemblies may also be used, for example, as an aid to an astronaut during maintenance activities when the astronaut is required to leave his or her aerospace vehicle to perform a specified activity, such as during the repair of a satellite or another aerospace vehicle.
Of course deployable structural assemblies have utilization in other circumstances as well, including, generally, situations where it would be inefficient to build a permanent structural assembly but where a structural member or assembly is required to provide additional height or to span a distance in order to place and/or support a given component or structure at a specified location. In one example, a deployable structural assembly may be used to position a bank of lights above a specified area such as in an emergency situation or in association with an outdoor concert or other activity. Similarly, a deployable structural assembly might be used to position an antenna or other communications device. In another example, one or more deployable structural assemblies may be used to support a raised platform which may serve as a working surface for one or more people.
Numerous configurations of deployable structural assemblies have been developed. For example, U.S. Pat. No. 3,503,164 issued to Berry et al., U.S. Pat. No. 3,543,806 issued to Rushing et al., U.S. Pat. No. 3,601,940 issued to Simon, U.S. Pat. No. 3,811,633 issued to Cummings et al., U.S. Pat. No. 6,345,482 issued to Warren, and U.S. Pat. No. 6,560,942 issued to Warren et al. each disclose various types of deployable structures.
The Berry et al. patent discloses a tubular extendable structure that is formed of a pair of elongated sheets which are pre-stressed in a predetermined manner so that they curl about their respective longitudinal axes when unrestrained. Each sheet includes a series of interlocking components formed along each longitudinal edge thereof for engagement with corresponding interlocking components formed in the other associated sheet. With the interlocking components of each sheet engaged with one another, the sheets may be flattened for rolling onto a drum and, when in the rolled state, they store energy associated with deforming the sheets from their pre-stressed state. Upon unrolling of the sheets, the stored energy causes them to resume their previous configuration including the exhibited curl about their longitudinal axes.
The Rushing et al. patent discloses an extendible boom formed of a single sheet of “springlike material” which may be rolled onto a reel for storage. When released from the reel, the sheet curls together edgewise and forms a hollow tubular shape as a rod or a boom. The edges of the sheet include tabs that may engage one another when the sheet is curled.
The Simon patent discloses a structure similar to that of the Rushing et al. patent wherein the joined edges of the material sheet form a helical seam about the resulting boom.
The Cummings et al. patent discloses a collapsible/extendible tubular structure having four walls wherein two oppositely disposed walls include a pair of elongated ribbons joined along their longitudinal edges to form a plurality of “cusps” which allow the structure to be folded flat and then wound into a coil.
The Warren and Warren et al. patents disclose an open lattice, foldable, self-deployable structure having longitudinal members configured to bend and diagonal members configured to bend and twist about certain axes. The structure is described as being folded or rolled without material yielding and as being “self resurrecting” during deployment.
While the above-listed U.S. Patents show various configurations of deployable structural assemblies, it is desirable to improve upon the deployable structural assemblies disclosed in the prior art with regard to various features. For example, it is desirable to provide a deployable structural assembly that enables efficient, simplified and reliable deployment and retraction. Additionally, it is desirable to provide a deployable structural assembly with an improved strength and stiffness to weight ratio while also being scalable in design such that various lengths, cross-sectional sizes and load capacities may be provided. It is also desirable to provide a deployable structural assembly that provides a significant reduction in stowed size and an improved packing factor as defined hereinbelow.